The law reads that the country's nuclear weapons are a "means of defence" and serve the purpose of "dealing deadly retaliatory blows at the strongholds of aggression until the world is denuclearised".

On Sunday the Workers' Party Central Committee held a rare high-level meeting in which it described nuclear weapons as "the nation's life".

"The DPRK [North Korea]'s possession of nuclear weapons should be fixed by law and the nuclear armed forces should be expanded and beefed up qualitatively and quantitatively," a KCNA report on the meeting said.

"The People's Army should perfect the war method and operation in the direction of raising the pivotal role of the nuclear armed forces in all aspects concerning war deterrence and war strategy."

In the last few days North Korea has issued multiple warnings of attacks on US and South Korean targets - to which the US has responded with an apparent show of military hardware. The US flew F-22 planes from Japan to South Korea's Osan Air base on Sunday, as part of ongoing joint military exercises with Seoul, officials said.

Speaking to defence officials on Monday, South Korean President Park Geun-hye said that she took the series of threats from Pyongyang "very seriously".

But despite its rhetoric few think the North - which last week cut a military hotline which was the last official direct link with Seoul - would risk full-blown conflict.

In Washington, President Barack Obama's spokesman that "despite the harsh rhetoric we are hearing from Pyongyang, we are not seeing changes to the North Korean military posture, such as large-scale mobilisations and positioning of forces".